Field of the Invention
The present disclosure relates to a structure, a method for manufacturing the structure, and a Talbot interferometer.
Description of the Related Art
Diffraction gratings having periodic structures are used as optical elements in various types of apparatus. In particular, structural bodies made of a metal having a high X-ray absorptance are used for nondestructive inspection, medical practice and the like.
One of the applications of structural bodies made of a metal having a high X-ray absorptance is the shield grating of interferometers (X-ray Talbot interferometers) for X-ray Talbot interferometry. The X-ray Talbot interferometry is a method for collecting the information of a subject using the phase shift of X-ray waves by the subject.
The X-ray Talbot interferometry will be simply described below. A typical X-ray Talbot interferometer diffracts coherent X-ray radiation through an X-ray diffraction grating to form an interference pattern. The X-ray shield grating, which is disposed at the position where the interference pattern is formed, blocks part of X-ray radiation that is to form the interference pattern, thus forming an intensity distribution different from that of the interference pattern. The information of this intensity distribution is obtained by detecting X-ray radiation from the X-ray shield grating with an X-ray detector. The intensity distribution is changed by disposing a subject in the light path between an X-ray source and the X-ray shield grating. The information of the subject is obtained from the change of the intensity distribution.
If an X-ray source that emits low-coherent X-ray radiation is used as a light source of a Talbot interferometer, an X-ray shield grating is disposed between the X-ray source and a diffraction grating so as to form imaginarily an array of micro-focus X-ray sources, and thus coherence is given to the X-ray radiation. This technique is particularly called X-ray Talbot-Lau interferometry. In the following description, the X-ray shield grating disposed at the position where an interference pattern is formed is referred to as an analysis grating; and the X-ray shield grating disposed between an X-ray source and a diffraction grating is referred to as a source grating. The X-ray shield grating simply mentioned refers to either a source grating or an analysis grating, or both.
A typical X-ray shield grating used for Talbot interferometry has a structure in which X-ray transmission portions (may be simply referred to as transmission portions) and X-ray shield portions (may be simply referred to as shield portions) are periodically arranged. The X-ray shield portions are often made of a metal having high X-ray absorptance. Even when the shield portions are made of a metal having a high X-ray absorptance, however, the shield portions are required to have a high aspect ratio from the viewpoint of the relationship between the thickness required to block X-ray radiation and the period of the interference pattern (for the analysis grating) or the imaginary array of X-ray sources (for the source grating). In the present disclosure or the description herein, the aspect ratio of the shield portions is defined as the ratio (h/w) of the height h of the shield portion to the width w thereof.
For manufacturing such a shield grating, a process is known in which a mold is filled with a metal by plating.
Japanese Patent Laid-Open No. 2010-185728 discloses a method for manufacturing a shield grating, in which a metal is deposited by plating in recessed portions formed in a silicon substrate by reactive etching.
In this method, after protective film is formed on the bottoms and side walls of the recessed portions, the silicon substrate is exposed at the bottoms, and the exposed surface of the silicon substrate is used as a seed layer for growing a metal therefrom.
The present inventors however have found that the adhesion between the metal and the silicon substrate can be reduced depending on the metal and the magnitude of the film stress produced in the metal, and that the connection between the bottom of the recessed portion and the metal is broken in some cases by receiving a physical force.